This invention relates generally to compressor refrigeration systems such as employed in automobile air-conditioners, and is more specifically concerned with a new and unique construction for a surge tank for use with the compressor.
A typical automobile air-conditioning system comprises a closed refrigeration circuit containing a compressor, a condenser, and an evaporator. The evaporator comprises a heat exchange unit in which liquid refrigerant is allowed to expand and evaporate thereby absorbing heat from air passing across the heat exchange surface. The gaseous refrigerant containing the absorbed heat is drawn via the suction line into the compressor where it is compressed and then discharged via the discharge line to the condenser. The condenser comprises another heat exchange unit wherein the hot pressurized refrigerant is condensed into liquid by heat exchange action. The liquid refrigerant is then returned to the evaporator via the liquid line where it is once again allowed to expand. The compressor is driven by the engine to circulate refrigerant through the system, and additional devices and controls are associated with the system whereby the desired air-conditioning action takes place to the comfort of the occupants.
In operation the compressor produces a pulsating output. The output pulsations will fluctuate depending upon a number of factors such as the particular construction of the compressor and refrigeration system, the particular operating conditions, and the particular setting of associated controls. Therefore, it is desirable to minimize such fluctuations and one way to do so is by including a surge tank at the compressor outlet in the discharge line to the condenser. The surge tank is effective to dampen the fluctuations and thereby promote better operation. By minimizing fluctuations, peak pressures can be reduced, a more steady flow promoted, and noise can be attenuated. This promotes improved system operation and longer life for the components.
Previous techniques for making production surge tank bodies typically comprise fabrications from separate metal parts assembled together. One previous technique involves cutting a tube to a desired length and then assembling formed caps onto the ends of the tube. Another previous technique involves forming a heavy impact extrusion and then assembling a cap onto the open end of the extrusion. Welding and brazing are conventional operations used to join the separate parts.
Production surge tanks must meet very stringent requirements for refrigerant leakage. Because the previous techniques described above result in surge tank bodies having welded or brazed joints extending around their circumferences, a significant rejection rate in the production of such tanks occurs due to excessive refrigerant leakage through the joints.
In the case of a welded joint, the weldment may appear outwardly satisfactory but in fact may have minute pin holes which can give rise to excessive refrigerant leakage.
In the case of a surge tank one of whose parts is a heavy impact extrusion, the effectiveness of brazing is often impaired because of the manner in which the extrusion is made. In order to produce a satisfactory part, the extrusion process may require the application of a certain lubricant to the material being extruded. Such lubricant is difficult to remove from the extruded part and it is a hindrance to subsequent effective brazing.
Despite the significant rejection rates for production surge tanks which occur using the aforementioned techniques, these manufacturing procedures have been tolerated since no more effective ones have apparently been developed.
The present invention is directed to a new and improved construction for surge tanks of the type used in automobile air-conditioning systems. It offers a number of important advantages over the prior techniques described above.
Perhaps the most significant attribute of the invention is that the rejection rate for production surge tanks is significantly lowered because it yields surge tanks which are less susceptible to refrigerant leakage. This means a reduction in the amount of scrappage and rework required, leading to significant productivity improvements. This of course has important benefits for both manufacturer and consumer.
The fabrication process which is used in practice of the invention is itself efficient and a further contributor to productivity. For example, the prior technique of fabricating a heavy extrusion involves an appreciable energy expenditure merely to form the extrusion, and subsequent welding and/or brazing procedures are still necessary to join the several parts of the surge tank body.
The procedure involved with the present invention does not require the use of lubricants nor other materials which could have an adverse effect on the surge tank either during its fabrication process or subsequently.
Briefly the present invention involves the application of friction spinning to conventional tube stock to form the surge tank body. This procedure results in a surge tank in which the body is a unitary piece devoid of seams except at locations where tubes and/or fittings are assembled to the body. No special extrusion techniques or formed caps are required and therefore labor, material and fabrication costs can be reduced.
The invention also has the advantage that the fabrication process can be adapted to produce a surge tank body of a desired shape. This is an important consideration in the disclosed application in an automobile air-conditioning system because the arrangement of the automobile engine compartment in which the surge tank is located in association with the engine-driven compressor usually imposes severe constraints on the space available for the surge tank. With the present invention, the shape can be readily modified in a number of different ways which will become more apparent from the ensuing description. Different embodiments of the surge tank of the present invention are disclosed herein by way of examples and these may comprise bodies in which one or both end walls are formed by friction spinning.
The well known down-sizing and quality improvement efforts in the automobile industry also make weight savings and improved component performance important considerations.
The present invention, in addition to the advantages previously discussed, meets the objectives of using light-weight material, (aluminum or aluminum alloys are the preferred materials), and has an organization which efficiently uses material so as to favorably impact on the amount of material used. The finished product is better suited to the quality improvement effort of the industry than is the prior multi-piece body construction.
The foregoing features, advantages and benefits of the invention, along with additional ones, will be seen in the ensuing description and claims which should be considered in conjunction with the accompanying drawings. The drawings disclose a preferred embodiment of the invention according to the best mode contemplated at the present time in carrying out the invention.